JP2008069028A - Growing method of gallium nitride single crystal, and gallium nitride single crystal obtained by it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of increasing growing speed and yield for the growing of a gallium nitride single crystal by a sodium flux method. <P>SOLUTION: In this method, a strontium material is added to sodium less than 3 mol% in equivalent of strontium metal, that is, it is added in a minute quantity of X mol% wherein 0<X<3, based on the mol% of metal strontium. The growing speed of GaN single crystal in the direction of c axis is increased by about 3 times or more with the addition of 0.05 mol% and the yield is also increased by about 21 times with the addition of 0.03 mol% (b) compared with the case where only Na is used (a). Thus, with the addition of a minute quantity of strontium to the sodium flux, the yield of GaN single crystal can be increased to a large extent. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for growing a gallium nitride (GaN) single crystal suitably used as a substrate for electronic devices, particularly ultraviolet to infrared light emitting devices and power devices, and a gallium nitride single crystal obtained thereby.

  As light emitting devices and power devices as described above, GaN-based (GaN, InGaN, AlGaN, InAlGaN) semiconductors are attracting attention because high characteristics can be obtained. However, at present, the cost of high-quality GaN-based single crystal substrates is high, so devices are fabricated on dissimilar material substrates such as sapphire, silicon carbide, and silicon, and physical properties such as lattice constant and thermal expansion coefficient are large. Due to differences, high-quality devices cannot be fabricated.

Here, the main GaN substrate manufacturing methods include HVPE (Hydride Vapor Phase Epitaxy) for vapor phase growth, and high-pressure synthesis method, flux method, and ammonothermal method for liquid phase growth. Among them, although the HVPE method commercializes a 2-inch size crystal substrate, the dislocation density, which is one of crystal defects, is still 10 ⁶ / cm ² , and the cost is several tens of 10 for a 2-inch substrate. Since it is high from 10,000 yen to 1,000,000 yen, it is difficult to use it as a substrate for LED or LD.

On the other hand, in liquid phase growth, there is no growth method for producing GaN crystals as a commercial product at present, but the flux method and high-pressure synthesis method have a dislocation density of 10 ³ except for the ammonothermal method. It has been reported in papers, lectures, etc. that high quality crystals can be grown at / cm ² or less (Non-Patent Documents 1 to 3). Comparing the high-pressure synthesis method with high-quality crystal reports and the flux method, the growth conditions of the high-pressure synthesis method require an ultra-high temperature and high pressure of about 1500 ° C. and a pressure of about 10,000 atm. Then, the temperature is about 800 ° C. and the pressure is about 50 atmospheres, and the growth conditions are relatively gentle compared to the high pressure synthesis method. In addition, in the flux method, it has been reported that the addition of alkali metal Li or alkaline earth metal Ca to metal Na increases the yield and growth rate of GaN, which can reduce the cost. (Non-Patent Document 4).

Therefore, the present inventors previously proposed Patent Document 1, and according to the prior art, a large single crystal having a low dislocation density was obtained by adding lithium Li to the flux in the sodium flux method. Yes.
Jpn. J. Appl. Phys 42 (2003) L729 J. Cryst Growth 222, 431 (2001) Japanese Journal of Applied Physics Vol.44 No.52 L1570-L1572 J. Cryst Growth 284 (2005) 91-99 International Publication No. 2004/067814 Pamphlet

  However, in order to be widely used as a substrate for the LED or LD, it is necessary to further increase the growth rate and yield.

  An object of the present invention is to provide a method for growing a gallium nitride single crystal capable of increasing the growth rate and yield, and a gallium nitride single crystal obtained thereby.

  The method for growing a gallium nitride single crystal according to the present invention is a method for growing a gallium nitride single crystal by reacting an alkali metal melt containing gallium and a source gas containing nitrogen at a high temperature and high pressure. Sodium is selected, and a strontium material is added to the sodium in an amount of less than 3 mol% in terms of metal strontium.

  According to the above configuration, the gallium nitride single unit is prepared by reacting a melt containing gallium with an alkali metal and a source gas containing nitrogen atoms (for example, nitrogen gas, ammonia gas, or a mixed gas thereof) at high temperature and high pressure. In the method for growing crystals, when using a so-called sodium flux method in which sodium is selected as the alkali metal, strontium (Sr), which is one of the alkaline earth metals, is replaced with metal strontium with respect to the sodium as a flux component. In addition, as a compound containing the same, a very small amount of Xmol% in which 0 <X <3 is added in mol% based on metal strontium.

  As a result, the growth rate in the c-axis direction of the GaN-based single crystal is increased by about 3 times or more with the addition of 0.05 mol%, and the yield is also increased with the addition of 0.03 mol%, compared with the case of Na alone. About 21 times. Thus, by adding a small amount of strontium to the sodium flux, the yield of the GaN-based single crystal can be significantly increased.

  In addition, the method for growing a gallium nitride single crystal according to the present invention is characterized by adding about 0.03 mol% of metal strontium or a compound containing the same to the sodium in terms of metal strontium.

  According to the above configuration, as described above, only by adding a small amount of strontium to the sodium flux, the crystal growth rate increases and the yield also increases. However, the addition amount X is large, and the amount is 3 mol% or more. If it becomes, it will become no different from sodium simple substance, and the peak of a yield will appear in the said 0.03 mol% vicinity.

  Therefore, by setting X = 0.03 mol%, the maximum yield can be obtained without increasing the addition amount X unnecessarily.

  Furthermore, in the method for growing a gallium nitride single crystal according to the present invention, the strontium material is strontium nitride.

According to the above configuration, the strontium material may be a single metal strontium, but by using strontium nitride, the same additive amount X can be obtained without affecting the GaN-based single crystal in which the component of the compound is formed. Even in the case of adding, the weighing value increases, and the weighing error can be reduced. For example, when 0.03 mol% of metal Sr (atomic weight: 87.62) is used with respect to 4.4 g of metallic Na (atomic weight: 22.9898), it is necessary to weigh 5.00 mg. When Sr ₃ N ₂ (molecular weight: 290.86) is used, 5.53 mg is weighed at the same molar ratio. Further, in the case of SrGaN or strontium nitride, nitrogen is contained as a nitride, and when dissolved in the melt, the nitrogen concentration in the melt increases, and the GaN-based crystal is likely to grow.

  In the method for growing a gallium nitride single crystal of the present invention, the growth temperature is 500 to 1000 ° C., preferably 850 to 870 ° C., and the growth pressure is 30 to 65 atm, preferably 35 to 45 atm. To do.

  According to the above configuration, the growth rate can be increased at a relatively low temperature and pressure.

  Furthermore, the method for growing a gallium nitride single crystal according to the present invention is characterized in that a gallium nitride single crystal is used as a seed crystal and its a-plane or m-plane is used for growth.

  According to the above configuration, when strontium-added sodium is used as the flux, the growth rate in the c-axis direction is increased as described above as compared to the case of sodium alone or the case of adding other alkaline earth metal. Therefore, by utilizing the a-plane or the m-plane for growth, the coalescence of the crystal is promoted, and the crystal can have a large area.

  In the method for growing a gallium nitride single crystal according to the present invention, the crucible containing the starting alkali metal and the gallium material and the strontium material and dissolved in the melt is made of a material containing alumina, yttria, molybdenum, tungsten or tantalum. It is characterized by comprising.

  According to the above configuration, in the crystal growth in which another kind of metal is added to the alkali metal, the generated crystals increase, but most of them are crystals generated from the crucible wall surface. Therefore, when the crucible material is alumina, yttria, molybdenum, tungsten or tantalum, generation of crystals from the crucible wall surface can be suppressed, and only the introduced seed crystals can be grown. This makes it possible to grow large crystals efficiently.

  Furthermore, in the method for growing a gallium nitride single crystal according to the present invention, the atmosphere in which the alkali metal and strontium materials are weighed has an oxygen concentration of 20 ppm or less and a moisture value of 10 ppm or less.

  According to said structure, a metal strontium and an alkali metal react easily with the oxygen and the water | moisture content in air, and form an oxide and a hydroxide. These oxides and hydroxides are harmful in the flux method and inhibit the formation of GaN-based crystals. Therefore, when the glove box is kept at the oxygen concentration of 20 ppm or less and the moisture value of 10 ppm or less as described above, the formation of the oxide or hydroxide can be suppressed and the amount of GaN-based crystals generated can be increased. it can.

  The gallium nitride single crystal of the present invention is obtained by the above-described method for growing a gallium nitride single crystal.

  According to said structure, a growth rate and a yield can be increased significantly and a low-cost gallium nitride single crystal can be obtained.

  As described above, the method for growing a gallium nitride single crystal according to the present invention is one of the alkaline earth metals with respect to the flux component sodium when growing the gallium nitride single crystal using the so-called sodium flux method. As a metal strontium or a compound containing the same, strontium (Sr) is added in a very small amount of Xmol% that satisfies 0 <X <3 in mol% of the metal strontium base.

  Therefore, the growth rate in the c-axis direction of the GaN-based single crystal is increased about three times or more with the addition of 0.05 mol%, and the yield is also increased with the addition of 0.03 mol%, compared with the case of Na alone. About 21 times. Thus, by adding a small amount of strontium to the sodium flux, the yield of the GaN-based single crystal can be significantly increased.

  Further, in the method for growing a gallium nitride single crystal according to the present invention, as described above, when the addition amount X is large and the amount is 3 mol% or more, it becomes the same as sodium simple substance, and the yield peak is 0.03 mol. %, X = 0.03 mol%.

  Therefore, the maximum yield can be obtained without unnecessarily increasing the addition amount X.

  Furthermore, in the method for growing a gallium nitride single crystal according to the present invention, the strontium material is strontium nitride as described above.

  Therefore, the weighing value can be increased and the weighing error can be reduced without affecting the GaN-based single crystal in which the component of the compound is produced and also when the same addition amount X is added.

  In the method for growing a gallium nitride single crystal according to the present invention, as described above, the growth temperature is 500 to 1000 ° C., preferably 850 to 870 ° C., and the growth pressure is 30 to 65 atm, preferably 35 to 45 atm.

  Therefore, the growth rate can be increased at a relatively low temperature and pressure.

  Furthermore, in the method for growing a gallium nitride single crystal according to the present invention, as described above, when strontium-added sodium is used as a flux, the gallium nitride single crystal grows as compared with the case where only sodium is added or other alkaline earth metals are added. Since the growth rate in the axial direction increases, the a-plane or m-plane is used for growth.

  Therefore, the coalescence of the crystal is promoted, and the crystal can have a large area.

  In the method for growing a gallium nitride single crystal according to the present invention, the crucible material is alumina, yttria, molybdenum, tungsten, or tantalum as described above.

  Therefore, generation of crystals from the crucible wall surface can be suppressed, and only the introduced seed crystals can be grown. This makes it possible to grow large crystals efficiently.

  Furthermore, in the method for growing a gallium nitride single crystal of the present invention, as described above, metal strontium and alkali metal easily react with oxygen and moisture in the air to form oxides and hydroxides. The glove box is weighed while maintaining an oxygen concentration of 20 ppm or less and a moisture value of 10 ppm or less.

  Therefore, the formation of the oxide or hydroxide can be suppressed, and the amount of GaN-based crystals generated can be increased.

  In addition, the gallium nitride single crystal of the present invention is obtained by the method for growing a gallium nitride single crystal as described above.

  According to said structure, a growth rate and a yield can be increased significantly and a low-cost gallium nitride single crystal can be obtained.

  FIG. 1 is a diagram showing a schematic configuration of an experimental apparatus 1 for explaining a method for growing a gallium nitride single crystal according to an embodiment of the present invention. This experimental apparatus 1 is configured such that an electric furnace 3 and various pipes 4, 5, 6, an instrument 7, and the like are housed in a glove box 2. Stop pipes 8, 9, and 10 are interposed in the pipes 4, 5, and 6, respectively, and the pipes 4, 5, and 6 are connected to the SUS tube 11, the vacuum pump 12, and the gas cylinder 13, respectively. The pipes 5 and 6 are connected to each other and can be attached to and detached from the pipe 4 by a joint 14.

In the experiment, metal Ga as a starting material, metal Na and metal Sr serving as a flux, GaN seed crystal, and crucible 21 were placed in the glove box 2 and the stop valve 9 was opened with the joint 14 opened. The stop valve 10 is shut off, and the inside of the glove box 2 is once evacuated using the vacuum pump 12, then the stop valve 9 is shut off, the stop valve 10 is opened, and gas is supplied from the gas cylinder 13. By doing so, the inside of the glove box 2 is replaced with Ar or N ₂ , and the oxygen concentration is controlled to 20 ppm or less and the moisture value is 10 ppm or less. Thereafter, the oxidized portion of Na or Sr in the flux is removed using a metal knife, and only the portion with metallic luster is weighed together with the metal Ga as the starting material, and put into the crucible 21 with a predetermined weight described later.

The crucible 21 containing these fluxes and starting materials is housed in a SUS tube 11 together with a GaN seed crystal, sealed, and removed from the glove box 2 so as not to come into contact with air. The stop valve 8 is connected to the SUS tube 11, and the presence of the stop valve 8 allows connection to the gas cylinder 13 without being exposed to the atmosphere. Subsequently, the SUS tube 11 is installed in the electric furnace 3, the joint 14 is connected, and the stop valve 10 is opened while the stop valves 8 and 9 are shut off, so that the gap between the gas cylinder 13 and the SUS tube 11 is established. After replacing the pipes 4 and 6 with N ₂ gas, the stop valve 8 is opened, and N ₂ gas is introduced into the SUS tube 11 through a pressure regulator (not shown).

  After pressurizing to a predetermined pressure, for example, 30 to 65 atm, by the pressure regulator, the temperature of the electric furnace 3 is raised to a growth temperature, for example, 500 to 1000 ° C., preferably 850 to 870 ° C. in several hours. A GaN single crystal is grown from the GaN seed crystal by entering the period and maintaining the temperature during the period (more preferably, at about 850 ° C., 35 to 45 atm). The growing period may be set according to the amount of the starting material and the crystal size to be grown, and is usually about 100 to 150 hours.

  At the end of the growing period, energization of the electric furnace 3 was stopped, the stop valves 8 and 10 were shut off, the temperature of the electric furnace 3 was lowered to about room temperature, and the internal pressure of the glove box 2 was lowered to normal pressure. Thereafter, the joint 14 is cut off, the SUS tube 11 is further cut, and the crucible 21 is taken out.

  Thereafter, by allowing the grown crystal to penetrate the crucible 21 containing the flux and residual metal into ethanol and water, the metals Na and Sr react with ethanol and water to be removed. Subsequently, the metallic Ga that has not become a GaN crystal is removed using concentrated hydrochloric acid or the like, and then the crystal is taken out, whereby the GaN single crystal can be produced. Furthermore, a GaN substrate can be produced by performing mechanical polishing to flatten the obtained crystal.

  It should be noted that in the present embodiment, when growing a GaN-based single crystal by the sodium flux method as described above, the Sr, which is one of the alkaline earth metals, is added to the flux component Na. In addition, when the addition amount is X mol% based on the metal Sr with respect to the metal Na, the minute amount range of 0 <X <3 is set.

  Table 1 shows the experimental results of the present inventors, and shows the growth rate in the c-axis direction of a GaN single crystal when an alkaline earth metal is added to the flux of the alkali metal Na. First, among alkaline earth metals, Be and Ra are dangerous and cannot be used. Therefore, when comparing Mg, Ca, Sr, and Ba, when the same mol% of Mg is added, the growth rate is 5 to 10 μm / h, which is about the same as that of Na alone. On the other hand, the growth rates of Ca and Ba are slightly higher than the previous Mg, although the conditions are slightly different from the current conditions as in the previous application of the present inventors. In addition, when alkali metal Li, which is reported in the paper, is added to Na, the growth rate in the c-axis direction is almost the same as that of Na alone.

  On the other hand, it is understood that the growth rate in the c-axis direction of the GaN single crystal when the metal Sr is added is greatly increased, for example, about 3 times as compared with the case of only Na. . Specifically, after 150 hours of growth, the growth length in the c-axis direction is 1.85 mm as shown in FIG. 2 (a) with Na alone, and as shown in FIG. 2 (b) when Sr is added. It was 5 mm.

  Table 2 and FIG. 3 also show the experimental results of the present inventors, and show the change in the yield of the GaN single crystal when the mol% of Sr is changed. From Table 2 and FIG. 3, the yield is greatly increased by adding a small amount of Sr, and the peak is about 21 times when 0.03 mol% is added. It is understood that there is no.

  Furthermore, in growing, a seed crystal is used and its a-plane or m-plane is used for growth. This is because when a seed crystal is used, generation of new nuclei is prevented, and the introduced seed crystal itself grows efficiently and a large crystal is obtained. In particular, when the flux is made of a plurality of materials, nucleation is likely to occur, which is preferable. Further, when the strontium-added sodium is used as the flux, the growth rate in the c-axis direction is increased as described above compared to the case of sodium alone or the case of adding other alkaline earth metal. This is because by using the m-plane for growth, the coalescence of the crystal is promoted, and the crystal can have a large area.

Here, as a material of the seed crystal, Al _x Ga _y In _1-xy N can be used, for example, a GaN template formed on a sapphire substrate by MOCVD method or HVPE method, or A GaN-based single crystal without sapphire obtained by a flux method is desirable. These GaN-based seed crystals may be put in the crucible 21 together with the flux and the starting material, but are introduced after the nitrogen is sufficiently dissolved in the melt and the melt is in the metastable region, and after the growth. It is desirable to lower the temperature or pressure after removing the grown seed crystal from the melt.

  In the case of InAlGaN crystal, the a-plane is (2-1-10), (11-20), (-12-10), (-2110), (-1-120), (11-20). ) Planes, planes parallel to the respective planes, or planes inclined within ± 45 ° with respect to the planes, and the m plane is (1-100), (10-10), (01-10) ), (−1100), (−1010), (0-110) plane, a plane parallel to each of those planes, or a plane inclined within ± 45 ° with respect to each plane.

  FIG. 4 shows a photograph of crystals grown by the present inventors. Both a-plane templates made of GaN were grown. FIG. 4 (a) shows the case where a flux containing only Na is used, and FIG. 4 (b) shows a flux obtained by adding 0.03 mol% of Sr. Shows the case. From FIG. 4A and FIG. 4B, a rectangular and large-area crystal is obtained by using a flux containing Sr.

  As described above, according to the present embodiment, by adding a small amount of Sr by the sodium flux method, the growth rate and yield in the c-axis direction are greatly increased compared to Mg, Ca, and Li. can do. In particular, when X = 0.03 mol% as described above, the maximum yield can be obtained without increasing the addition amount X unnecessarily. Note that the optimum value of the addition amount X varies slightly depending on the growth temperature, pressure, material of the crucible 21, and the like.

  Further, according to the present embodiment, the growth temperature is 500 to 1000 ° C., preferably 850 to 870 ° C., and the growth pressure is 30 to 65 atm. Therefore, the growth rate is increased at a relatively low temperature and pressure. Can do.

  Furthermore, according to the present embodiment, Ga and Sr are weighed in the glove box 2 and the atmosphere thereof is set to an oxygen concentration of 20 ppm or less and a moisture value of 10 ppm or less, so that those oxides that inhibit the formation of GaN. And the generation of hydroxides can be suppressed, and the amount of GaN produced can be increased.

The metal Sr may be previously placed in the crucible 21 together with other fluxes and starting materials as described above, or may be added during the experiment. As the nitrogen source gas, ammonia (NH ₃ ) containing nitrogen atoms, a mixed gas of the ammonia and pure nitrogen (N ₂ ) gas, or the like can also be used.

The strontium material may be the metal strontium alone, but it is preferable to use strontium nitride instead of metal strontium. In this case, the components of those compounds do not affect the GaN-based single crystal to be produced, and even when the same addition amount X is added, the weighing value increases and the weighing error can be reduced. . For example, when 0.03 mol% of metal Sr (atomic weight: 87.62) is used with respect to 4.4 g of metallic Na (atomic weight: 22.9898), it is necessary to weigh 5.00 mg. When Sr ₃ N ₂ (molecular weight: 290.86) is used, 5.53 mg is weighed at the same molar ratio. In addition, SrGaN and strontium nitride contain nitrogen as a nitride, and when dissolved in the melt, the concentration of nitrogen in the melt increases and GaN can easily grow.

  Furthermore, the crucible 21 is preferably made of a material containing alumina, yttria, molybdenum, tungsten or tantalum. This is because, in crystal growth in which other kinds of metals are added to an alkali metal, the number of generated crystals increases, but most of them become crystals generated from the wall surface of the crucible 21, and BN (B: In the case of a crucible made of boron, N nitrogen (BN boron nitride), about 1.35 g of GaN was generated from the crucible wall at the experimental conditions mainly used at this time of about 850 ° C. and 40 atm. Therefore, when the material of the crucible 21 is alumina, yttria, molybdenum, tungsten, or tantalum, generation of GaN crystals from the wall surface of the crucible 21 can be eliminated, and large crystals can be grown efficiently. These materials may be used for all of the crucible 21 or may be used only for the portion that comes into contact with the melt.

  The size of the crucible 21 used in this experiment is approximately 20 mm in outer diameter, 18 mm in inner diameter, and 20 to 50 mm in height. In the case of alumina and yttria, such a shape can be molded by a sintered body, and in the case of molybdenum, tungsten and tantalum, it can be molded by deforming these metals to the above size. .

It is a figure which shows schematic structure of the experimental apparatus for demonstrating the growth method of the gallium nitride type | system | group single crystal which concerns on one Embodiment of this invention. It is a drawing substitute photograph of the crystal which this inventor grew. It is a graph which shows the experimental result of this inventor. It is a drawing substitute photograph of the crystal which this inventor grew.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Experimental apparatus 2 Glove box 3 Electric furnace 4, 5, 6 Piping 7 Instrument 8, 9, 10 Stop valve 11 SUS tube 12 Vacuum pump 13 Gas cylinder 14 Joint 21 Crucible

Claims (9)

In a method for growing a gallium nitride single crystal by reacting a melt containing gallium with an alkali metal and a source gas containing nitrogen at high temperature and high pressure,
A method for growing a gallium nitride single crystal, wherein sodium is selected as the alkali metal, and a strontium material is added to the sodium in an amount of less than 3 mol% in terms of metal strontium.   2. The method for growing a gallium nitride single crystal according to claim 1, wherein about 0.03 mol% of metal strontium or a compound containing the metal is added to the sodium in terms of metal strontium.   2. The method for growing a gallium nitride single crystal according to claim 1, wherein the strontium material is strontium nitride.   The growth temperature is 500 to 1000 ° C., and the growth pressure is 30 to 65 atm, The gallium nitride single crystal growth method according to claim 1, wherein the growth temperature is 30 to 65 atm.   The method for growing a gallium nitride single crystal according to claim 4, wherein the growth temperature is 850 to 870 ° C. and the growth pressure is 35 to 45 atm.   The method for growing a gallium nitride single crystal according to any one of claims 1 to 5, wherein a gallium nitride single crystal is used as a seed crystal, and the a-plane or m-plane is used for growth.   7. The gallium nitride-based single unit according to claim 6, wherein the crucible containing starting alkali metal and gallium material and strontium material and dissolved in the melt is made of a material containing alumina, yttria, molybdenum, tungsten or tantalum. Crystal growth method.   The method for growing a gallium nitride single crystal according to any one of claims 1 to 7, wherein an atmosphere in which the alkali metal and the strontium material are weighed has an oxygen concentration of 20 ppm or less and a moisture value of 10 ppm or less.   A gallium nitride single crystal obtained by the method for growing a gallium nitride single crystal according to any one of claims 1 to 8.